In a formation of various patterns included in a semiconductor device, a photo-lithography process using a photoresist may be implemented. For example, a photoresist layer may be divided into an exposed portion and a non-exposed portion by an exposure process. Either of the exposed portion and the non-exposed portion may be removed by a developing process to form a photoresist pattern. An object layer may be etched using the photoresist pattern as a mask to form a desired pattern.
During the exposure process, chemical structures and properties of the photoresist layer may be changed by a chemical reaction occurring in the photoresist layer.